hal@finney.org wrote:
> How would the towers cool? Would they be painted white to reflect
> sunlight, or is there some other effect? Takes a mighty big air
> conditioner...
It contains the updraft and allows it to more efficiently transport heat to the top of the troposphere. The upper surface of the resultant cloud (it doesn't work as well without condensation) then radiates to space (as well as reducing the insolation on the area around the tower). Rain would fall downwind as well as inside the tower.
> I ask because I have seen claims that towers would, in and of
> themselves, produce cool air updrafts because as the air rises
> it expands, hence it cools.
Yes, but as moisture condenses, the air cools much more slowly (wet adiabatic vs dry adiabatic), and because it is much warmer than the air outside the tower, it is less dense, powering the updraft. The updraft is relatively warm, moving heat from the surface into space.
> However this does not work, because the same effects occur
> in the atmosphere outside the towers, which is why mountains are
> cooler than valleys. So I wonder if these cooling towers in Analog
> had some other principle in mind.
By reducing mixing (thermals separate from their warm source on the surface and become vortex rings which ingest cool air from their surroundings) the tower encourages a much greater mass (and heat) flow than would naturally occur. It's merely a damn big chimney- and large chimneys can "draw" on a sunny day even when the brickwork is *cooler* than the inlet air. Poor heat transfer makes the flow nearly adiabatic despite the presence of the cold walls. I once saw a large abandoned chimney (a large door open in its base) drawing strongly on a warm day- no wind, cold bricks.
-- Doug Jones, Rocket Plumber